Wall Street Journal reporter Evan Gershkovich stands in a glass cage in a courtroom on April 18 at the Moscow City Court, in Moscow, Russia. Alexander Zemlianichenko/Associated Press

HELSINKI —President Biden on Thursday said he’s serious about pursuing a prisoner exchange for a Wall Street Journal reporter who has been detained in Russia for more than 100 days.

The Kremlin earlier this month suggested that it was open to a possible prisoner exchange that could involve Evan Gershkovich, a 31-year-old Bowdoin College graduate, but it underscored that such talks must be held out of the public eye.

Speaking at a news conference in Helsinki, Finland, Biden made clear that the U.S. is interested.

“I’m serious on a prisoner exchange,” said Biden, who was concluding a five-day visit to Europe that took him to the UK, Lithuania, and Finland. “And I’m serious about doing all we can to free Americans being illegally held in Russia or anywhere else for that matter, and that process is underway.”

Gershkovich was arrested on espionage charges in the city of Yekaterinburg while on a reporting trip. He is being held at Moscow’s Lefortovo prison, notorious for its harsh conditions. A Moscow court recently upheld a ruling to keep him in custody until Aug. 30.

Gershkovich and his employer deny the allegations, and the U.S. government has declared him to be wrongfully detained. His arrest rattled journalists in Russia. Authorities there have not provided any evidence to support the espionage charges.

White House national security adviser Jake Sullivan confirmed last week that there have been “discussions” between the two sides, but cautioned that there is not yet “a clear pathway” to winning Gershkovich’s freedom.

Gershkovich is the first American reporter to face espionage charges in Russia since September 1986, when Nicholas Daniloff, a Moscow correspondent for U.S. News and World Report, was arrested by the KGB. Daniloff was released 20 days later in a swap for an employee of the Soviet Union’s U.N. mission who was arrested by the FBI, also on spying charges.

In Washington, the Wall Street Journal and Gershkovich’s family have sought to keep the spotlight on his detention.

At a National Press Club event on Thursday, Gershkovich’s sister, Danielle, described the emotional toll from her brother’s captivity. “I just try to take it day by day. It still feels unreal sometimes. For my parents, it’s a full-time job.”

She said she had received a letter from him just this week.

One silver lining of the 100th-day marker, she said, was the publicity and attention for her brother.

“Seeing Evan’s face in the news was just really heartening. At such a dark time, it’s wonderful to see his face again.”